NEW YORK — Retailers are reporting surprisingly weak December revenue after a strong November pulled forward holiday spending and a blizzard in the Northeast took a bite out of sales after Christmas.

The results raise some worries that the holiday season might be less stellar than some had hoped, but some analysts still expect spending in November and December to show the largest annual increase since 2006.

As merchants report their figures Thursday, many retailers including Target Corp., Costco Wholesale Corp. and Macy's Inc. reported gains below Wall Street expectations. Bon-Ton Stores Inc.'s sales were virtually flat and company officials blamed the severe snowstorms.

The figures are based on revenue at stores opened at least a year and are considered a key indicator of a retailer's health.

"It's not shaping up to be a blowout holiday for retailers. It's slow and steady," said Ken Perkins, president of RetailMetrics.

The disappointing December figures were surprising given earlier data from MasterCard Advisors' SpendingPulse and anecdotal evidence that pointed to a strong December. But Perkins still thinks overall holiday revenue, which combines November and December, will show the strongest increase since 2006.

Costco Wholesale Corp.'s sales at warehouse clubs open at least a year climbed 6 percent in December. The figure was a bit below the 6.2 percent rise that Thomson Reuters predicted.

Target Corp. said that it revenue at stores open at least a year rose 0.9 percent, well below the 4 percent increase that Thomson Reuters expected. Strength in groceries and clothing was offset by weakness in electronics, toys and some home categories.

Sales for key gift categories were pulled forward into November, Target Chairman and CEO Greg Steinhafel said in a statement, and merchandise with lower profit margins made up a higher portion of sales than expected.

Macy's revenue at stores opened at least a year rose 3.9 percent, below the 4.5 percent estimate. But the combined November and December figure rose 4.6 percent. The company is sticking to its profit outlook for the fourth quarter.